Asus boosts USB transfer speeds with new SCSI-based protocol

On Asus’s new motherboards — the P8Z77-V and some of its contemporary cousins — there’s an intriguing new feature: USB attached SCSI protocol, or UASP for short. Asus says that UASP can almost double the speed of USB 3.0 connections to external hard drives and SSDs — and speed up the transfer rate of older USB 2.0 connections, too.

In essence, UASP modernizes the USB transfer protocol. Despite USB 1.1 being introduced way back in 1998, USB 2.0 and 3.0 still use the same Bulk-Only Transport (BOT) protocol for mass storage I/O. Without getting into complexities, BOT is a very simple/dumb protocol. With 12Mbps USB 1.0 and 480Mbps USB 2.0 — generally a lot slower than most external storage solutions — BOT never really reared its ugly head. USB 3.0 has a max data rate of 4.8Gbps, however — and it turns out that BOT isn’t a good protocol if you’re pushing hundreds of megabytes per second from an SSD or a VelociRaptor.

UASP does away with BOT and replaces it with something akin to SCSI, a protocol that is much better suited to low-latency bulk data transfers (pictured right). In reality, according to benchmarking performed by Hot Hardware, the speed boost is nowhere near the 70% that Asus claims, but a more modest 5-20%. Curiously, the largest speed-up is on intra-drive copying — so if you use an external SSD or HDD as your Photoshop scratch disk, or some other task that involves moving files around on an external storage array, UASP could provide a significant speed boost. The boost should also become more apparent as drive speed increases, too — or if you have an external array of drives that push the 4.8Gbps capacity of USB 3.0.

The one caveat of UASP, as you can imagine, is that it requires a UASP-compatible controller on both the motherboard and on the external enclosure. For the time being, this means you’ll need an Asus motherboard with a compatible Asmedia USB controller, and also an external enclosure with an Asmedia controller (such as the Thermaltake ST0019U).

If you don’t want to replace your current enclosure, however, Asus does have a fall-back: UASP-equipped motherboards also come with “Turbo” mode, which is basically an optimized version of BOT — instead of waiting for acknowledgement of commands (as per the diagram above), Turbo just keeps sending commands, in theory reducing latency and improving performance. In Hot Hardware’s benchmarks, Turbo mode was mediocre, boosting performance in some tests but negligible in others.

Read more about UASP at Asus — but equip your anti-rose-tinted spectacles first

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cool to hear that usb transfer today is now faster compared to previous. Now we have choices on that to make our file transfer faster. Thanks for sharing this wonderful post. Now I know that there’s a way to make fast in transferring file via usb.

rickcain2320

Why didn’t the industry just adopt firewire? That was such a great interface and had none of the bad habits of USB.

http://www.mrseb.co.uk/ Sebastian Anthony

Because it was EXPENSIVE :) USB is much cheaper — that’s the only real reason.

deere92

finally; USB gets where ethernet has been since replacing half-duplex with full-duplex 10 years ago or something…

Mark Hahn

First of all, the main point of UASP is concurrent transactions. If you’re talking to a normal disk, your concurrency will be limited (often limited by the usb-to-sata bridge to 1). But in principle, a normal sata disk can support a queue depth of 32, which usually permits some useful head-scheduling.

And UASP for flash is a huge win, since even flash sticks these days often have multiple channels.

Also, is the author sure that the USB controller on the motherboard needs anything special to support UASP? I’ve been able to use UASP under linux on a wide variety of non-cutting-edge boards and laptops. After all, UASP has been in the standard since before USB3…

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